Electron tube



NM. 15, 1938. w. FEDERMANN 5% AL 2,137,202

ELECTRON TUBE Filed July 20, 1934 ATTORNEY Patented Nov..15, 1938 V PATENT OFFICE ELECTRON 1 Wolfgang Federmann and Johannes Richter,

Berlin, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphic ni. b. 11., Berlin, Germany, a corporation of Germany -Application July 20, 1934, Serial No. 736,192' InGermany July 28, 1933 I 6 Claims T (c1. 25o 141 The invention relates to measuresoncathode ray type tubes having a concentrated cathode ray, in particular for television purposes, for the purpose of eliminating the disturbances caused by the so-called zero point anomaly.

High vacuum, as Well as gas filled cathode ray tubes, frequently show the so-called zero point anomaly whose physical causes are not at present completely ascertained. The zero point anomaly is perceptible at the oscillograph operation with cathode ray tubes by-a bending of the luminous line on the luminous screen at the place at which the cathode ray in-the-presence of a field-free space would impinge in the tube.

Television pictures produced by means of cathode ray tubes are frequently disturbed by the zero point anomaly in such a way that the horizontal lines are more strongly contrasted-at the place of the zero point anomaly producing, due to the decrease of the dark intermediate line spaces, a

greaterbrightness of the picture field. In the vertical direction of the picture field the zero liancy of each line at 34 mm. The intersection point of these lines appearingas a bright cross upon a darker background in the-picture, is the resting position of the cathode ray in the fieldiree space of the tube.

With the usual type of cathode ray tube, a further detrimental effect on the picture caused by the zeropoint anomaly resides in that the vertical edge of the picture receives .a depression at the place of the horizontalzero point anomaly (i. e. at the height of the horizontal line of the tion point of the zero point anomaly-cross is placed outside the picture field. Thus, it is necessary to place the point of impingement on the I screen of the ray. passing through the field free space, at the edge of the screen. Although it is possible to displace the picture field on the screen 'by means of magnetic fields, yet the disturbing bright cross remains at the same place or line in the picture field and will be displaced simultaneously therewith. Furthermore, it is possible to displace the ray towards the edge of the screen by an oblique arrangement of the neck of the bulb at the conical part of the bulb. In connecting, as usual, always one of the plates of the two pairs of deviation plates electrically to the anode, and applying to the opposite plates positive or'negative control'voltages with respect to the anode, the zero point anomaly still appears in the picture field, namely ,at'the place which corresponds with" the deviation by the voltage which is equal to the voltagedrop of the cathode ray on the way between anode and deviation plates as is already known in the art. 7

Furthermore, experiments have been carried out in which it was found that the zero point anomaly does not occur at electromagnetic deviation, but only at electrostatically controlled deviation. However, the gained experience teaches fundamentally that the anomaly appearing at electrostatical. deviation cannot be eliminated by electroma'gnetical influences but only by electrostatical influences.v

' The present invention shows ways in which the disturbing zero point anomaly can be withheld from the picture and to increase thereby essentially the quality of the picture. The means are partially of mechanical and electrical nature. In most cases the mechanical means always require again, thecorrection by electrical means. If negative as well as positive potentials measured with respect to the anode are applied to the deviation plates producing the picture screen, the picture field canbe so displaced on the screen thatit lies only in one quadrant of the bright cross produced by the zero point anomaly; i. e. in placing the resting'point of the ray in a corner. of thepicturefield .or outside the-picture field, the zero point anomaly does not'appear.

The invention is illustrated in several of its forms by, the accompanying-drawing. wherein:

Fig. 1 andFigurela show one form of system for eliminating the zero point anomaly;

Fig. 2 represents a modification wherein the electrode system is inclined to provide for correction of the zero'point;

Fig. 3 showsan'inclined arrangement of defiectingplates;

- Fig. 4 illustrates a modification of inclined electrodearrangements; and,

Fig. 5 illustrates one means for adjusting the electrode positions,

Referencemay now be made to the drawing for a complete understanding of the invention. One convenient method by which the displacement of the resting point of the fluorescent spot on the luminous screen may be obtained by means of additional deviation plates is that which is shown by Fig. 1 wherein the cathode ray tube R in two projections in a schematical illustration is shown. K designates the cathode, W is the Wehnelt cylinder and A represents the anode, P1, P2 are the pairs of deviation or deflection plates serving for the control of the coordinates (screen plates) and P3 designates a further correspondingly oriented pair of plates to which such a potential is applied that the electron ray S in its position of rest passes in a corner of the square determined by the planes of the screen plates P1, P2. If necessary, in place of one pair of plates P: two of them can be used. In this way it' is possible to displace the resting position of the fluorescent spot L into the periphery of the picturescreen. This method can also be used in the case of a bent glass bulb in accordance with the explanation of operation above given, whereby the displacement of the resting position relative to the picture field will be obtained to the greater. part by the shaping of the bulb.

A further measure for eliminating the zero point anomaly resides in causing the electron ray to pass in an inclined direction to one or several electrodes. To this end, various parts of the electrode system can be. obliquely placed with respect to the axis established by the screen plates. In particular the following possibilities are to be mentioned: Inclination of the axis of the Wehnelt cylinder towards the axis of the system; inclination of the axis of the plate or tubularly shaped anode towards the axis of the system; and inclination of the centrally aligned system consisting of cathode Wehnelt cylinder and anode, towards the axis of the screen plates as is shown particularly by Fig. 2.

In all these measures the danger exists that the electron ray passing through the tube in an oblique direction may brush the edge of a screen plate in particular that of the pair near the screen. In order to avoid this, it is suggested in accordance with the invention instead of arranging as usual the screen plates parallel to each other at least those of the outer most pair, to dispose them inclined to each other and in such manner that the opening of the angle enclosed by the planes of the plates, faces the screen as shown by Fig. 3.

A special mode of arranging an anode coming within the scope of the invention is shown in Fig. 4 by way of example. The anode in this arrangement consists of a plate a. at right angles vto the axis of the system, and a tubular portion a attached obliquely thereto. In order to explain the action of the inclined position of the anode it is pointed out that the latter influences the electrons in the manner of a lens due to the course of the neighboring equipotential surfaces, so that an oblique position of the anode causes a change in the direction of the ray.

It will be readily conceived that the angles of inclination to be resorted to must be accurately maintained in mounting the electrode system, and that a certain difliculty in the manufacture is thereby encountered. In order to overcome such difficulty, it is herewith proposed to fasten the above mentioned parts to be obliquely disposed to a body consisting of a glass or metal spring which is sealed into the tube and can be adjusted in its position from the outside. In this manner the optimum angle of inclination can be accurately adjusted later on. An example of an embodiment is schematically represented in Fig. 5. The electrode system of Fig. 5 consists of cathode K, Wehnelt cylinder W and anode A The press member Q is supported corrugated sheet metal) and is preferably welded onto a tube R. By means of a small rod or tubing St the desired inclination can be imparted to the electrode system.

In an obliquely disposed anode tubing in ac- 'cordance with Fig. 4 the angle of inclination can be adjusted in an advantageous manner in that the tubing is produced of a wire wound as helix and which again can be displaced from the outside by means of a springy member molten into the wall of the vessel.

Havingv thus described the invention, what we claim is:

1. Cathode ray tube structure comprising an envelope, means for producing a concentrated electron ray including a cathode, an anode, a Wehnelt focusing cylinder, a luminescent screen, symmetrical means for controlling the deflection of the ray in two mutually perpendicular directions, the axis of symmetry of said symmetrical means coinciding axially with the cathode, and at least one of the elements included in the means for producing the concentrated electron ray having its axis inclined with respect to the axis of the envelope for imparting to the electron ray an eccentrical position of rest both in the space enclosed by the planes of the deflection means and upon the screen.

2. Cathode ray tube structure as claimed in claim 1 characterized further in that the axis of the anode electrode and of the focusing Wehnelt cylinder are obliquely diposed to each other.

3. Cathode ray tube structure of the character defined by claim 1 further characterized in that the common axis of the cathode concentration electrode and anode is inclined toward the axis of the deviation plates.

4. Cathode ray tube structure as claimed in claim 1 wherein the anode electrode consists of a flat disk member having an obliquely mounted tubular portion.

5. Cathode ray tube structure as claimed in claim 1 further characterized by the fact that the anode electrode consists of a tubing obliquely mounted within the tube in combination with means capable of movement from without the tube for adjusting the position of the tubular member.

6. Cathode ray tube structure as claimed in claim 1 wherein at least one pair of beam deflection electrodes are inclined toward each other.

WOLFGANG FEDERMANN. J OH. RICHTER. 

